One hundred eighty-seven glial malignancies have been generated in 128 offspring of 14 pregnant F-344 rats treated transplacentally with the resorptive, neurotropic carcinogen, ethylnitrosourea (ENU). In order to generate glioma lines for immunological experiments, 83 of such gliomas have been processed for (a) tumor cell cultures, and (b) direct transplantation passages or alternate culture-to-animal passages to subcutaneous and intracerebral sites of syngeneic, sex-matched recipients. Direct transplantation of ENU-induced gliomas to the intracerebral site of new hosts has yielded successful growths which have maintained the morphological features of parent glial tumors. Passage of ENU-induced gliomas to the subcutaneous site of new hosts either directly or by means of alternate culture-to-animal passage has yielded growths that, in a high proportion of cases, contain sarcomatous elements. Immune reactions against ENU-induced gliomas in vivo and in vitro are being investigated and experiments are being designed to determine the source of sarcomatous elements in subcutaneous glioma transplants.